Absorbent article with back sheet, and method for manufacturing the back sheet

ABSTRACT

There is disclosed an absorbent article including: a liquid-permeable top sheet; a back sheet; and an absorbent core sandwiched between the top sheet and back sheet. The back sheet is formed of a resin film containing an inorganic filler in a resin base material. The back sheet includes: a stretched moisture-permeable region; and a high optical transmittance region having a lower degree of orientation than that of the moisture-permeable region and/or left unstretched.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an absorbent article such as adisposable diaper, a sanitary napkin, a pantie liner or a urineabsorbing pad and, more particularly, to an absorbent article using aback sheet having regions, which are different in the degree oforientation, and a method for manufacturing the back sheet.

[0003] 2. Related Art

[0004] In order to absorb discharges, there have been recently employeda number of absorbent articles such as disposable diapers, sanitarynapkins, pantie liners or urine absorbing pads. When a discharge is madewhile the absorbent article is worn, the absorbent article havingabsorbed the discharge is disposed of and is replaced by a new one.

[0005] Here, the back sheet to be ordinarily employed in the absorbentarticle is exemplified by a liquid-impermeable resin sheet. The backsheet is formed by stretching a resin film containing an inorganicfiller so as to enhance the air-permeability and themoisture-permeability so that the back sheet is made opaque. In the caseof the diaper, therefore, in order to confirm whether or not the wearerhas made a discharge, the care taker has to remove the diaper from thewearer to confirm the inside of the diaper. This is a seriouslytroublesome work for the care taker.

[0006] In Unexamined Published Japanese Patent Application No. 5-168660,therefore, there is disclosed a uniaxially oriented air-permeable filmwhich is embossed to have a moisture-permeability of 1,000 g/m²/24 hrsor more so as to enhance the optical transmittance. In this film,however, the moisture-permeability is not so lowered that the opticaltransmittance cannot be enhanced so high.

[0007] In Unexamined Published Japanese Patent Application No. 10-85257,on the other hand, there is disclosed a back sheet of a developing typedisposable diaper. In this back sheet, a see-through portion is formedin at least a central portion in the longitudinal direction. This backsheet is formed like before of a porous sheet, which is prepared bystretching the resin film containing the inorganic filler, for enhancingthe moisture-permeability. In the see-through portion, a transparentportion is formed by crushing the pores of the porous sheet by anembossing treatment thereby to eliminate the scattering of light. If theporous sheet is further embossed, however, pin holes will be easilyformed, because the embossed portion is lowered in its strength. Thereis also a description that the transparent portion could be formed byapplying wax, varnish or hot melt in place of the embossing treatment.However, the applied material will ooze or stick on the film surface andrequires a drying treatment after applied, so that the cost for thematerial and for the treatment rises.

[0008] Thus in the disposable diaper, there has been demanded a backsheet which is so enhanced in the optical transmittance that whether ornot the discharge has been made can be confirmed from the outsidewithout lowering the air-permeability, the moisture-permeability or thestrength.

[0009] Here will be described a sanitary napkin. This sanitary napkinmay be provided on the two longitudinally extending sides with wingswhich extend in the width direction. When the sanitary napkin is worn,the wings are folded back to the lower side of the crotch portion of theunderwear such as panties so that the edge portions of the panties canbe prevented from being blotted with the discharge. Moreover, the napkincan be prevented from going out of position by adhesion means disposedon the wings for attaching the napkin to the panties. These wings areformed by protruding the member constructing the body of the napkin,such as the adhered back sheet and top sheet, in the width directionfrom the two side portions of the body of the napkin.

[0010] In the back sheet of the sanitary napkin, however, the back sheetis formed as in the diaper by stretching the film so as to enhance theair-permeability so that the optical transmittance is extremely lowered.When the panties wearing the napkin with the wings is seen from theoutside, therefore, the presence of the wing portions, i.e., the wearingof the napkin is apparent from the outside. Only the wings could be madeof a material different from that of the back sheet, such as a highoptical transmittance sheet so that the wearing of the napkin could notbe confirmed in the appearance. However, this makes the manufactureprocess complex to raise the cost.

[0011] Thus, the absorbent article has been desired to have a partiallyhigh optical transmittance. However, the portion desired to have a highoptical transmittance is different among the kinds of absorbentarticles.

SUMMARY OF THE INVENTION

[0012] An object of the invention is to provide an absorbent articleusing a back sheet which has a high optical transmittance portion and anair- and moisture-permeable portion.

[0013] Another object of the invention is to provide a method formanufacturing the back sheet.

[0014] According to an aspect of the invention, there is provided anabsorbent article comprising: a liquid-permeable top sheet; a backsheet; and an absorbent core sandwiched between the top sheet and backsheet, wherein the back sheet is formed of a resin film containing aninorganic filler in a resin base material, and wherein the back sheetincludes: (a) a stretched moisture-permeable region; and (b) a highoptical transmittance region having a lower degree of orientation thanthat of the moisture-permeable region and/or left unstretched.

[0015] In the absorbent article of the invention, there are formed inone back sheet the high optical transmittance region and the high air-and moisture-permeable region. As a result, the high opticaltransmittance region can be formed in a portion of the absorbent articlewhile the air-permeability and the moisture-permeability being retainedin the entire absorbent article. In the diaper, for example, whether ornot the discharge has been made can be confirmed from the outside of thediaper being worn. In the sanitary napkin, the presence of the wingscannot be seen from the outside of the panties. Moreover, this strengthof the back sheet is hard to degrade.

[0016] The resin base material is preferably a polyolefin resin.

[0017] The mixing ratio between the resin base material and theinorganic filler is preferably 20 to 70% by mass: 80 to 30% by mass.

[0018] In the case where the absorbent article is a disposable diaper,the high optical transmittance region (b) is preferably positioned tocover the entirety or a portion of the back of the absorbent core. Inthis case, furthermore, the high optical transmittance region (b) ispreferably provided in the generally widthwise central portion of theregion having the absorbent core and in the region containing thewidthwise center of the absorbent core and having one quarter of thewidth size of the diaper, and/or in the generally longitudinal centralportion of the region having the absorbent core and in the regioncontaining the longitudinal center of the absorbent core and having onequarter of the longitudinal size of the diaper.

[0019] It should be noted that: the term “longitudinal centralportion/region” as used herein means the intermediate portion/regionlocated between two end regions lying opposite one another in thelongitudinal direction; the term “widthwise central portion/region” asused herein means the intermediate portion/region located between twoside regions lying opposite one another in the width wise direction. Itshould be also noted that: the term “longitudinal center” as used hereinmeans the midpoint located between two end edges lying opposite oneanother in the longitudinal direction; the term “widthwise center” asused herein means the midpoint located between two side edges lyingopposite one another in the widthwise direction.

[0020] In the case where the absorbent article is a sanitary napkinincluding a pair of wing portions disposed on the two sides of theregion of the absorbent core and extending outwardly in the widthwisedirection, on the other hand, the moisture-permeable region (a) ispreferably positioned to cover the entirety or a portion of the back ofthe absorbent core whereas the high optical transmittance region (b) ispreferably positioned in at least the wing portions. In this case,furthermore, the moisture-permeable region (a) is preferably positionedin the generally widthwise central portion of the region having theabsorbent core and over one half or more of the width size of theabsorbent core, and/or in the generally longitudinal central portion ofthe region having the absorbent core and over one half or more of thelongitudinal size of the absorbent core.

[0021] The moisture-permeable region (a) is preferred to have amoisture-permeability of 1,000 g/m²/24 hrs or more.

[0022] The moisture-permeable region (a) is preferred to have a totaloptical transmittance of 50% or less according to JIS-K-7105.

[0023] The high optical transmittance region (b) is preferred to have atotal optical transmittance of 60% or more according to JIS-K-7105.

[0024] If the back sheet in the moisture-permeable regions (a) has athickness T1 and if the back sheet in the high optical transmittanceregion (b) has a thickness T2, it is preferred that the values T1 and T2satisfy the following Formulas:

20≦{(T2−T1)/T1}×100≦30.

[0025] The back sheet may have a multi-layered structure in at least thehigh optical transmittance region (b).

[0026] The back sheet to be used in the absorbent article of theinvention can be formed simply at a low cost. According to anotheraspect of the invention, there is provided a method for manufacturing aback sheet for an absorbent article including: a liquid-permeable topsheet; the back sheet; and an absorbent core sandwiched between the topsheet and back sheet. A film containing an inorganic filler in a resinbase material is partially stretched to form: (a) a stretchedmoisture-permeable region; and (b) a high optical transmittance regionhaving a lower degree of orientation than that of the moisture-permeableregion and/or left unstretched.

[0027] In the above, a film being continuously fed may be stretchedexclusively at a central portion in a width direction (or in CD) thereofto form the moisture-permeable region (a) at the central portion.

[0028] In an alternative, a film being continuously fed may be stretchedexclusively on two side portions in a width direction (or in CD) thereofto form the moisture-permeable regions (a) on the two side portions.

[0029] In another alternative, a film being continuously fed may bepartially stretched at a predetermined interval in a longitudinaldirection (or in MD) thereof to form the moisture-permeable regions (a)at a spacing in the longitudinal direction.

[0030] In still another alternative, a film being continuously fed maybe partially stretched at a predetermined interval in a width direction(or in CD) thereof to form the moisture-permeable regions (a) at aspacing in the width direction.

[0031] The film may be stretched by an embossing treatment to form themoisture-permeable region (a).

[0032] It is possible that a film having partially different thicknessesis formed of a material containing the inorganic filler in the resinbase material and is stretched to form the moisture-permeable region (a)in the thinner portion and the high optical transmittance region (b) inthe thicker portion.

[0033] It is also possible that an unstretched film is partially coatedwith a transparent film and is then stretched to form themoisture-permeable region (a) in the portion, which is not coated withthe transparent film, and the high optical transmittance region (b) inthe portion which is coated with the transparent film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a top plan view, as taken from the back side, of adiaper as an absorbent article according to one embodiment of theinvention;

[0035]FIG. 2 is a section taken along line II-II of the diaper shown inFIG. 1;

[0036]FIGS. 3A, 3B and 3D are sections of a portion of a film beforeoriented, and FIGS. 3C and 3E are sections of a portion of a resin sheetafter oriented;

[0037]FIG. 4A is a perspective view for explaining a state in which thefilm is embossed, and FIG. 4B is a section of a portion of embossingrolls;

[0038]FIG. 5 is a top plan view, as taken from the back side, of adiaper according to another embodiment of the invention;

[0039]FIG. 6 is a top plan view, as taken from the back side, of adiaper according to still another embodiment of the invention;

[0040]FIG. 7 is a top plan view, as taken from the back side, of asanitary napkin as an absorbent article according to still anotherembodiment of the invention;

[0041]FIG. 8 is a section taken along line VIII-VIII of the sanitarynapkin shown in FIG. 7; and

[0042]FIG. 9 is a top plan view of a portion showing a state in whichthe sanitary napkin shown in FIG. 7 is attached to panties.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043]FIG. 1 is a top plan view, as taken from the back side, of adiaper as an absorbent article according to one embodiment of theinvention, and FIG. 2 is a section taken along line II-II of the diapershown in FIG. 1. Here, the longitudinal direction of the diaper is takenin a Y-direction, and the widthwise direction generally perpendicular tothe Y-direction is taken in an X-direction.

[0044] A disposable diaper 1A, as shown in FIG. 1, is the so-called“open type” diaper and is constructed, as shown in FIG. 2, to include: aliquid-permeable top sheet 4 to confront the wearer; aliquid-impermeable back sheet 3; and an absorbent core 2 sandwichedbetween the top sheet 4 and the back sheet 3. These top sheet 4, backsheet 3 and absorbent core 2 are individually formed into the hour glassshape. However, the absorbent core 2 may have a rectangular shape. Thetop sheet 4 and the back sheet 3 are adhered and jointed to each otherat the outer sides of the absorbent core 2 in the X-direction and in theY-direction by means of a hot-melt type adhesive, for example.

[0045] For example, the top sheet 4 is made of nonwoven fabriccomprising hydrophobic fibers subjected to a hydrophilic treatment orhydrophilic fibers, such as point bond, air-through, spun bond or spunlace nonwoven fabric. The top sheet 4 has a basis weight (this may bereferred to as “METSUKE”) of 10 to 40 g/m². Moreover, the top sheet 4may be formed by laying a cushion layer of bulky nonwoven fabric overthe former nonwoven fabric. On the other hand, the absorbent core 2 isformed of an absorbent material, for example, pulverized pulp or amixture of pulverized pulp and a highly water-absorbing polymer, whichis enveloped with an absorbent sheet of tissues.

[0046] On the other hand, the diaper 1A may be provided with leg cuffsfor ensuring the close contact around the legs, although not shown, andleakage preventing cuffs 8 for preventing sideway leakage, as shown inFIG. 2.

[0047] The liquid-impermeable back sheet 3 is made of a resin sheetwhich is prepared by orientating a resin film containing an inorganicfiller to have regions different in the degree of orientation. In orderto reduce the uncomfortableness of the wearer, the diaper 1A may beprovided with a nonwoven fabric layer on the outer side (i.e., on thelower side of the back sheet 3, as seen in FIG. 2) of the back sheet 3(of the resin sheet). In this modification, the nonwoven fabric to beemployed has a high moisture-permeability and a high opticaltransmittance so as not to impair the functions of regions (a) and (b),which will be described hereinbelow, of the back sheet 3 (of the resinsheet).

[0048] This back sheet 3 is different in properties between itswidthwise central region 31 containing the center line 30 of the diaper1A and its two adjoining side regions 32 and 32. Specifically, these twoside regions 32 and 32 are moisture-permeable regions (a) having arelatively high moisture-permeability, whereas the central region 31 isa region (b) (as hatched in FIG. 1) having a higher opticaltransmittance than the moisture-permeable regions (a).

[0049] When the wearer of the diaper 1A makes a discharge, thisdischarge is absorbed mainly at the widthwise central region 31 of theabsorbent core 2 of the diaper 1A. Since this central region 31 has thehigh optical transmittance, the discharge can be discriminated in itscolor, when absorbed by the absorbent core 2, from the outside of thediaper 1A through the back sheet 3. Thus, it can be easily confirmedwhether or not the wearer has discharged.

[0050] At this region (b) of the high optical transmittance, the resinsheet constituting the back sheet 3 is formed by either not orientatingthe film or orientating the film at a low degree of orientation. In theregion (b), therefore, the optical transmittance is kept so high or notdegraded as can confirm the color of the discharge which was absorbed bythe absorbent core 2. The region (b) is preferred to have a totaloptical transmittance of 60% or more according to JIS-K-7105. Thisstandard is preferably satisfied even when the nonwoven fabric layer islaminated on the outer side of the resin sheet. Here, the region (b) hasa low moisture-permeability because it has few pores.

[0051] At the two side regions 32 and 32, on the other hand, the resinsheet is formed by orientating the film at a higher degree oforientation than that of the region (b) so that the opticaltransmittance is lower than that of the region (b) whereas themoisture-permeability is made higher in the presence of the pores. Evenwith the region (b) of the low moisture-permeability being present inthe central region 31, therefore, the inside of the diaper 1A does notbecome stuffy so that the wearer does not have a rash. For this effect,the moisture-permeable regions (a) are preferred to have amoisture-permeability of 1,000 g/m²·24 hrs or more. This standard ispreferably satisfied even when the nonwoven fabric layer is laminated onthe outer side of the resin sheet.

[0052] The moisture-permeability is measured by the following method(according to JIS Z-0208).

[0053] (1) 20 ml of water is poured into a cup having a radius of 0.03m.

[0054] (2) The cup is put in a cup-shaped bed a size larger than thecup, and the cup-shaped bed is covered at its mouth with a film, themoisture-permeability of which is to be measured. Then, the edge of thefilm and the edge of the cup-shaped bed are sealed up with heated wax(e.g., a mixture of (yellow) beeswax and (white) paraffin at 6:4). Thus,a sample is obtained.

[0055] (3) This sample is allowed to stand for 24 hrs in a constanttemperature/moisture apparatus (at 20° C. and 60% RH), and the weight ofthe sample is then measured (to have a value A).

[0056] (4) The sample is allowed to stand for 24 hrs in a constanttemperature/moisture apparatus (at 40° C. and 60% RH) and then for 30minutes in a constant temperature/moisture apparatus (at 20° C. and 60%RH), and the weight of the sample is measured (to have a value B).

[0057] The moisture-permeability is calculated from the followingFormula by applying the values A and B obtained:

Moisture-Permeability (g/m²·24 hrs)

=(B−A)/(π×0.03×0.03).

[0058] When the absorbent article of the invention is exemplified by thediaper 1A shown in FIG. 1, the width size of the region (b) (or thecentral region 31) in the X-direction is preferred to be within about 30to 70% of the entire width of the film. With the region (b) being formedover such range, the discharge can be reliably recognized. In addition,the diaper 1A hardly becomes stuffy in its inside.

[0059] Any resin base material for the resin sheet can be employed, buta polyolefin resin is preferably used for the aspects of cost andsafety.

[0060] As this polyolefin resin, there can be enumerated polypropylene,low-density polyethylene (LDPE), high-density polyethylene, linearlow-density polyethylene (LLDPE), polybutene, ethylene-propylenecopolymer, ethylene-butene copolymer and ethylene-vinylacetatecopolymer. At least one kind of these can be employed. Of these, thepreferable one is the LDPE, and the more preferable one is the LLDPE.

[0061] As the inorganic filler, there can be enumerated barium sulfate,barium carbonate, calcium sulfate, calcium carbonate, magnesiumhydroxide, magnesium oxide, aluminum hydroxide, zinc oxide, titaniumoxide, silica and talc. Of these, barium sulfate, calcium carbonate andmagnesium hydroxide are preferable. To the resin, there can be added anultraviolet ray absorbent, an oxidation inhibitor, an stabilizer, acoloring agent, a lubricant and so on.

[0062] The mixing ratio between the resin base material and theinorganic filler is preferably 20 to 70% by mass: 80 to 30% by mass. Ifthe inorganic filler is more than the upper limit, the resin filmbecomes clouded in white before oriented so that it cannot form theregion (b) having the high optical transmittance. If the inorganicfiller is less than the lower limit, on the other hand, pin holes areformed when the resin film is oriented. More preferably, the ratio ofthe inorganic filler is 60 to 30% by mass.

[0063] The polyolefin resin and inorganic filler thus far specified and,optionally, other additives are mixed by using a Henschel mixer, a supermixer, a tumbler type mixer or the like and is kneaded into pellets bythe ordinary single- or double-screw extruder. Next, after anotherpelletized polyolefin resin is added, if necessary, those pellets aremelted at a melting point or higher of the base resin, preferably at atemperature higher than the melting point +20° C. and lower than thedecomposition temperature, and filmed into a resin film by using ainflation molding machine or a T-die molding machine. At this time, thematerial may be directly filmed by the extruder without beingpelletized. This resin film preferably has a thickness of 10 to 90 μm(microns). Under the above-specified lower limit, the film is liable tobreak in the subsequent orientation. Over the upper limit, no specialproblem arises, but the productivity is slightly lowered.

[0064] The resin film thus prepared is oriented in at least onedirection by the well-known method such as the roll method or the tendermethod to produce a resin sheet having the moisture-permeable regions(a) of the high moisture-permeability and the region (b) of the highoptical transmittance. The orientation is preferably uniaxialorientation in the X-direction (CD: Cross Direction) of 1.1 to 2.5times.

[0065] In order to prepare the resin sheets having the regions (a) and(b), for example, a film 50 a having a uniform thickness, as shown inFIG. 3A, is partially stretched to form a resin sheet 60 b, as shown inFIG. 3B. In this resin sheet 60 b, there are formed: themoisture-permeable regions (a) of the high moisture-permeability whichwere stretched to a smaller thickness; and the high opticaltransmittance region (b) which substantially retains the thickness ofthe resin sheet 50 a before stretched. Here, the film 50 a beforestretched is preferable to have a basis weight of 20 to 40 g/m².

[0066] In an alternative, as the film to be stretched, use can be madeof a film 50 c having a thicker portion 51 c and thinner portions 52 cas shown in FIG. 3C, which is formed by a corrugated die in theformation of the film. This film 50 c may be stretched in its entiretyto form the resin sheet 60 b, as shown in FIG. 3B. Even if the film 50 cis stretched in its entirety, the thicker portion 51 c is not changed inits substantial thickness, so that its optical transmittance is notlowered. On the other hand, the thinner portions 52 c are sufficientlystretched to form the moisture-permeable regions (a) of the highmoisture-permeability. Here, the film 50 c before stretched is preferredto have a basis weight of 40 to 50 g/m² in its entirety.

[0067] In another alternative, the resin sheet may be formed such that:a film (or resin) 53 d is laid over a portion of a film 54 d having auniform thickness, as shown in FIG. 3D; and the film 54 d is thenstretched like that shown in FIG. 3C to form a resin sheet 60 e, asshown in FIG. 3E. At this time, the portion laminated with the film 53 dprovides the high optical transmittance region (b) in the resin sheet 60e. It is preferable to employ a transparent film having a high opticaltransmittance as the film 53 d.

[0068] Here, in order to develop the different functions in the regions(a) and the region (b), the orientation is preferably performed suchthat the values T1 and T2 satisfy the following Formulas, if the resinsheet in the high moisture-permeable regions (a) has a thickness Ti andif the resin sheet in the high optical transmittance region (b) has athickness T2:

20≦{(T2−T1)/T1}×100≦30.

[0069] The aforementioned orientation may be performed separately atmultiple stages or in two or more directions including the X-directionand the Y-direction. The biaxial orientations are preferred to besimultaneously made. These biaxial orientations enhance the strength ofthe resin sheet.

[0070] The following embossing treatment can be additionally enumeratedas the means for forming the regions (a) and the region (b) by makingthe degree of orientation partially different in the resin film.

[0071] In FIG. 4A, a similar film 58, as continuously fed, is pinched byembossing rolls 70 a and 70 b so that it is pressed and stretched toform a resin sheet 68 having the regions (a) and the region (b). Theembossing rolls 70 a and 70 b are corrugated, in FIG. 4B, in thesurfaces of their two side regions. The film 58 is pinched and pressedby those corrugations so that it is stretched to form the regions (a).

[0072] When the film is embossed while being heated, however, the pinholes are liable to be formed in the film. Moreover, since the film isshrunken if embossed in the heated state, there arises another problemthat the film size is liable to warp. When the orientation is made bythe embossing treatment, therefore, care should be taken to hold thedegree of orientation by considering those problems.

[0073] Thus, the back sheet having the high moisture-permeable regions(a) and the high optical transmittance region (b) in the invention canbe manufactured simply and at a low cost from one material (i.e., onefilm). Unlike the case in which the back sheet is formed as in the priorart by partially mounting members of a different material, on the otherhand, a series of works from the formation of the back sheet to thecompletion of the absorbent article can be performed by carrying thefilm orienting step on the assembly line of the absorbent article.

[0074]FIG. 5 is a top plan view, as taken from the back side, of adiaper of another embodiment of the invention, and FIG. 6 is a top planview, as taken from the back side, of a diaper of still anotherembodiment of the invention.

[0075] In a diaper 1B shown in FIG. 5, there are formed in the widthwisecentral region 31 of the diaper a plurality of high opticaltransmittance regions (b) which are continuously extended in theY-direction at a predetermined spacing in the X-direction from eachother. In the central region 31, the regions (a) are formed between theregions (b) extending in the Y-direction. Therefore, the diaper 1B notonly can reliably recognize whether or not the discharge has been made,like the diaper 1A shown in FIG. 1, but also has a highermoisture-permeability in its entirety than that of the diaper 1A. Whenthe regions (a) are thus formed in the stripe shape, they may bearranged alternately with the regions (b) all over the surface of theback sheet 3.

[0076] In a diaper 1C shown in FIG. 6, on the other hand, unlike theforegoing diapers 1A and 1B having the regions (b) throughout the wholelength, the high optical transmittance region (b) is formed all over thewidth size in the X-direction of the diaper in the longitudinal centralregion 36 containing the center line 35 of the diaper. This resin sheetcan be obtained by stretching the film, as fed in the MD, at apredetermined spacing in the MD. Alternatively, the diaper 1C may bemanufactured by laminating the resin sheet, as can be prepared to havethe high optical transmittance region (b) at the center region in the CDby the methods shown in FIGS. 3 to 4, over the absorbent core and thetop sheet such that the MD may be in the X-direction.

[0077] In the case where the absorbent article is exemplified by thediaper, in order to confirm whether or not a discharge was made,reliably from the outside, it is preferable that the high opticaltransmittance region (b) is provided in the generally widthwise centralportion of the region having the absorbent core 2 and in the regioncontaining the widthwise center of the absorbent core and having onequarter of the width size of the diaper and/or in the generallylongitudinal central portion of the region having the absorbent core andin the region containing the longitudinal center of the absorbent coreand having one quarter of the longitudinal size of the diaper.

[0078]FIG. 7 is a top plan view, as taken from the back side, of asanitary napkin as an absorbent article according to still anotherembodiment of the invention; FIG. 8 is a section taken along lineVIII-VIII of the sanitary napkin shown in FIG. 7; and FIG. 9 is a topplan view of a portion showing a state in which the sanitary napkinshown in FIG. 7 is attached to panties. Here, the longitudinal directionof the sanitary napkin or the absorbent article is taken like before inthe Y-direction, and the widthwise direction generally perpendicular tothe Y-direction is taken in the X-direction.

[0079] A sanitary napkin 1E, as shown in FIG. 7, is generally symmetricwith respect to the center line Ly extending in the Y-direction. Thissanitary napkin 1E is provided, as seen from the section shown in FIG.8, with: a liquid-permeable top sheet 4 on the liquid receiving side; aliquid-impermeable back sheet 3 on the outer side; and an absorbent core2 sandwiched between the top sheet 4 and the back sheet 3. Theseindividual members are similar to those of the foregoing diapers. In thevicinity of the center line 35 located between two end edges lyingopposite one another in the Y-direction of the sanitary napkin,moreover, the top sheet 4 and the back sheet 3 are individually extendedin the X-direction to form wings 10 and 10.

[0080] As shown in FIG. 7, the sanitary napkin 1E is provided with anadhesive portion 12 on the back side of its body and adhesive portions13 on the back sides of the wings 10. The sanitary napkin 1E isattached, when worn, to the crotch portion 82 on the inner side ofpanties 80, as shown in FIG. 9. At this time, the adhesive portion 12 onthe back of the body is retained on the inner face of the crotch portion82 of the panties 80. Then, the wings 10, as extending outward of thebody in the X-direction, are folded along the edge portions 81 of thepanties 80 so that they are hooked on the panties 80 by the adhesiveportions 13. With these wings 10 thus provided, it is possible toprevent the edge portions of the panties from being blotted or thesanitary napkin 1E from going out of position.

[0081] In the back sheet 3 of this sanitary napkin 1E, the two sideregions 32 provide the high optical transmittance regions (b), and thecentral region 31 provides the high moisture-permeable region (a). Whenthe sanitary napkin 1E is attached to the panties 80, as shown in FIG.9, therefore, the wings 10 are so hardly prominent that the color of thepanties 80 can be seen through the wings 10. This makes the sanitarynapkin 1E unclear from the appearance. Here, the top sheet 4 used atthis time has to be high in the optical transmittance.

[0082] As in the foregoing diaper 1A, the regions (b) are preferred tohave a total optical transmittance of 60% or more according toJIS-K-7105. As in the diaper 1A, on the other hand, themoisture-permeable region (a) is preferred to have amoisture-permeability of 1,000 g/m²·24 hrs or more so as to prevent thepanties from becoming stuffy in its inside while wearing the sanitarynapkin 1E.

[0083] In the region (a), moreover, the total optical transmittance ispreferred to be 50% or less according to JIS-K-7105 so that the absorbedmensual blood may not be seen at the back side through the body of thesanitary napkin. It is, therefore, preferable that themoisture-permeable region (a), i.e., the low optical transmittanceregion is positioned at least in the generally widthwise central portionof the region having the absorbent core 2 and over one half or more ofthe width size of the absorbent core 2, and/or in the generallylongitudinal central portion of the region having the absorbent core 2and over one half or more of the longitudinal size of the absorbent core2.

[0084] In the region (a), the back sheet 3 is preferred to have atearing strength of 20 g or more so that it may be prevented from beingbroken by the adhesion of the adhesive portion 12 when the sanitarynapkin 1E is removed after use from the panties 80. In the regions (b),on the other hand, the back sheet 3 is preferred to have a tearingstrength of 200 g or more so that the wings 10 may be prevented frombeing torn from the body.

[0085] The wings 10 are preferred to have a rigidity at some level sothat they may be easily attached to the crotch portion 82 of the panties80. Therefore, the rigidity (as measured by the cantilever methodaccording to JIS L1096) of the regions (b) in the back sheet 3 ispreferably at 30 mm or higher.

[0086] Here, the region (a) and the regions (b) are given differentthicknesses so that the wings 10 are easily folded at their boundariesbetween the regions (a) and (b). Therefore, the sanitary napkin 1E canbe easily attached because the wings 10 are easily folded along the edgeportions 81 of the panties 80.

[0087] Here, the regions (b) need not be formed all over the two sideregions 32 but may be provided exclusively at the portions forming thewings 10.

[0088] The back sheet 3 of the sanitary napkin 1E can be prepared in amanner similar to that used in the aforementioned diaper. For example,the central region in the widthwise direction (or the CD) of the filmbeing fed may be exclusively embossed by using the embossing rolls 70 aand 70 b shown in FIG. 4A but having the corrugations of FIG. 4B attheir central portions.

[0089] In the back sheet of the absorbent article of the invention, itis possible to form the high optical transmittance region in a necessaryextension at a target portion. This back sheet should not be limited tothe open type diaper or the sanitary napkin thus far described but couldbe applied to another absorbent article such as a diaper, as formed inadvance into an underwear shape, a urine absorbing pad or a liner sheet.

[0090] In the absorbent article of the invention, as has been describedhereinbefore, there are formed in one back sheet the high opticaltransmittance portion (or the region (b)) and the high air- andmoisture-permeable portion (or the region (a)). In the diaper, forexample, the region (b) is formed-at the center so that whether or notthe discharge has been made can be confirmed from the outside of thediaper being worn. In the sanitary napkin, on the other hand, theregions (b) are formed in the wings so that the presence of the wingscannot be seen from the outside of the panties. As a result, the highoptical transmittance region can be formed in a portion of the absorbentarticle while the air-permeability and the moisture-permeability beingretained in the entire absorbent article. Moreover, the strength of theback sheet is hard to degrade.

[0091] According to the invention, on the other hand, the back sheethaving an optical transmittance changed partially can be manufactured ata low cost and with ease.

[0092] Here, comprises/comprising, when used in this specification istaken to specify the presence of stated features, integers, steps orcomponents but does not preclude the presence or addition of one or moreother features, integers, steps, components or groups thereof.

[0093] Although various exemplary embodiments have been shown anddescribed, the invention is not limited to the embodiments shown.Therefore, the scope of the invention is intended to be limited solelyby the scope of the claims that follow.

What is claimed is:
 1. An absorbent article comprising: aliquid-permeable top sheet; a back sheet; and an absorbent coresandwiched between said top sheet and back sheet, wherein said backsheet is formed of a resin film containing an inorganic filler in aresin base material, and wherein said back sheet includes: (a) astretched moisture-permeable region; and (b) a high opticaltransmittance region having a lower degree of orientation than that ofsaid moisture-permeable region and/or left unstretched.
 2. The absorbentarticle as set forth in claim 1, wherein said resin base material is apolyolefin resin.
 3. The absorbent article as set forth in claim 1,wherein the mixing ratio between said resin base material and saidinorganic filler is 20 to 70% by mass: 80 to 30% by mass.
 4. Theabsorbent article as set forth in claim 1, wherein said absorbentarticle is a disposable diaper, and wherein said high opticaltransmittance region (b) is positioned to cover the entirety or aportion of the back of said absorbent core.
 5. The absorbent article asset forth in claim 4, wherein said high optical transmittance region (b)is provided in the generally widthwise central portion of the regionhaving said absorbent core and in the region containing the widthwisecenter of said absorbent core and having one quarter of the width sizeof said diaper, and/or in the generally longitudinal central portion ofthe region having said absorbent core and in the region containing thelongitudinal center of said absorbent core and having one quarter of thelongitudinal size of said diaper.
 6. The absorbent article as set forthin claim 1, wherein said absorbent article is a sanitary napkinincluding a pair of wing portions disposed on the two sides of theregion of said absorbent core and extending outwardly in the widthwisedirection, and wherein said moisture-permeable region (a) is positionedto cover the entirety or a portion of the back of said absorbent corewhereas said high optical transmittance region (b) is positioned in atleast said wing portions.
 7. The absorbent article as set forth in claim6, wherein said moisture-permeable region (a) is positioned in thegenerally widthwise central portion of the region having said absorbentcore and over one half or more of the width size of said absorbent core,and/or in the generally longitudinal central portion of the regionhaving said absorbent core and over one half or more of the longitudinalsize of said absorbent core.
 8. The absorbent article as set forth inclaim 1, wherein said moisture-permeable region (a) has amoisture-permeability of 1,000 g/m²·24 hrs or more.
 9. The absorbentarticle as set forth in claim 1, wherein said moisture-permeable region(a) has a total optical transmittance of 50% or less according toJIS-K-7105.
 10. The absorbent article as set forth in claim 1, whereinsaid high optical transmittance region (b) has a total opticaltransmittance of 60% or more according to JIS-K-7105.
 11. The absorbentarticle as set forth in claim 1, wherein if the back sheet in themoisture-permeable regions (a) has a thickness T1 and if the back sheetin the high optical transmittance region (b) has a thickness T2, thevalues T1 and T2 satisfy the following Formulas: 20≦{(T2−T1)/T1}×100≦30.12. The absorbent article as set forth in claim 11, wherein said backsheet has a multi-layered structure in at least said high opticaltransmittance region (b).
 13. A method for manufacturing a back sheetfor an absorbent article including: a liquid-permeable top sheet; saidback sheet; and an absorbent core sandwiched between said top sheet andback sheet, wherein a film containing an inorganic filler in a resinbase material is partially stretched to form: (a) a stretchedmoisture-permeable region; and (b) a high optical transmittance regionhaving a lower degree of orientation than that of saidmoisture-permeable region and/or left unstretched.
 14. The back sheetmanufacturing method as set forth in claim 13, wherein a film beingcontinuously fed is stretched exclusively at a central portion in awidth direction (or in CD) thereof to form said moisture-permeableregion (a) at said central portion.
 15. The back sheet manufacturingmethod as set forth in claim 13, wherein a film being continuously fedis stretched exclusively on two side portions in a width direction (orin CD) thereof to form said moisture-permeable regions (a) on said twoside portions.
 16. The back sheet manufacturing method as set forth inclaim 13, wherein a film being continuously fed is partially stretchedat a predetermined interval in a longitudinal direction (or in MD)thereof to form said moisture-permeable regions (a) at a spacing in saidlongitudinal direction.
 17. The back sheet manufacturing method as setforth in claim 13, wherein a film being continuously fed is partiallystretched at a predetermined interval in a width direction (or in CD)thereof to form said moisture-permeable regions (a) at a spacing in saidwidth direction.
 18. The back sheet manufacturing method as set forth inclaim 13, wherein the film is stretched by an embossing treatment toform the moisture-permeable region (a).
 19. The back sheet manufacturingmethod as set forth in claim 13, wherein a film having partiallydifferent thicknesses is formed of a material containing the inorganicfiller in the resin base material and is stretched to form themoisture-permeable region (a) in the thinner portion and the highoptical transmittance region (b) in the thicker portion.
 20. The backsheet manufacturing method as set forth in claim 13, wherein anunstretched film is partially coated with a transparent film and is thenstretched to form said moisture-permeable region (a) in the portion,which is not coated with said transparent film, and said high opticaltransmittance region (b) in the portion which is coated with saidtransparent film.